Nogo inhibits neurite outgrowth by acting at the myelin surface through a neuronal surface receptor, NgR. Therapies targeting the Nogo-NgR pathway show promise in the treatment of spinal cord injury and other central nervous system diseases. However, much remains unknown regarding Nogo's function in uninjured cells. Nogo is a member of the Reticulon family, a conserved set of endoplasmic reticulum (ER)-associated proteins with unclear functions. The bulk of Nogo expression is intracellular rather than surface-associated. Additionally, Nogo is prominently expressed in neurons as well as in oligodendrocytes. These facts argue for other roles played by Nogo besides inhibiting axon growth. We have obtained data suggesting that Nogo isoforms regulate intracellular traffic. Furthermore, Nogo levels affect the specialized neuronal trafficking pathway of axon transport. Nogo may mediate its effects on traffic through small GTPases of the Rab family. Additionally, Nogo may affect trafficking of its own receptor, thereby creating a form of NgR regulation that has not previously been explored. Finally, Nogo may enhance neuronal survival in the context of motor neuron disease. Better understanding of these roles is crucial as therapies are being developed to block the Nogo pathway in the treatment of central nervous system injury. The Aims of this proposal are to further explore the mechanisms of Nogo's involvement in intracellular trafficking using a variety of cell imaging and biochemical techniques. Nogo's effects on the specialized neuronal trafficking pathways of axon transport and synaptic vesicle recycling will be explored with live cell imaging studies in neurons from wild type and Nogo-knockout mice. These studies will be performed under the mentorship of Dr. Stephen M. Strittmatter, a leader in the field of neuroregeneration and axonal signal transduction. He and his extremely well-funded laboratory provide the optimal setting for developing expertise in the techniques required for successful neuroscientific research. Furthermore, Yale's Department of Neurology has committed to fostering the applicant's development by limiting clinical responsibilities to allow at least 85% effort devoted to research, and by keeping open laboratory space available as the applicant transitions to running an independent laboratory during the period of this proposal. The Nogo pathway is intensely studied for its role in blocking injured nerves in the brain and spinal cord from regenerating. However, this proposal shows that Nogo also plays important roles that may help uninjured nerves function. Insight into these roles will shed light on Nogo's involvement in diseases like amyotrophic lateral sclerosis, and will help guide the development of safer therapies to inhibit the Nogo pathway in the context of spinal cord injury and other devastating central nervous system diseases.